Note: Descriptions are shown in the official language in which they were submitted.
1046815
BACKGROUND OF THE IN~'ENTION
Field of the Invention
This invention relates to the manufacture of
paper and is concerned with a method of increasin~ the
content of mineral f~llers (also known as loadings) in
paper sheet.
Descrl~tion of the Prior Art
In the manufacture of paper sheet it is customary
to incorporate in the aqueous paper pulp (also known
as the furnish) before it is transferred to the continuous
wire mesh (known as the "wire") at the wet end of the
papermaking machine a mineral filler the purpose of which
is primarily to improve the surface of the paper for
printing purposes and to reduce the production costs.
However there is a practical limit to the amount of filler
which can be employed in this manner owing to the fact
that as filler content increases the tens~le strength of
the paper sheet decreases. This is because the filler
particles interfere with the hydrogen bonding between
cellulose fibres and because with increased filler content
there is less fibre present in the paper sheet to impart
strength thereto.
It is known to incorporate, normally ~ust
ahead of the wire~ small amounts of polymeric materlals
in the dilute aqueous paper pulp/filler suspensions known
as "thin stock" to give improved retention of the
filler on the wire during sheet formation and hence improve
_2- ~
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.
1046815
the efficiency of the papermaking process by reducing filler
losses, generally referred to as white water losses.
Por instance, British Patent Specification No. 883~973
describes the use as a retention aid of trace amounts
of a water-soluble non-cationic linear vinyl polymer
having a molecular weight of at least 5 x 106 and at least
predominantly composed of carbamoylalkylene linkages
containing not more than 4 carbon atoms, the polymer
being added to the filler-containing aqueous suspension
of cellulose fibres prior to sheet formation on the wire.
British Patent Specification No. 1,353,015
describes a method of reducing the chemical reactivity
of calcium carbonate filler in a papermaking process
involving sizing under acid conditions~ such as the
traditional rosin soap/papermakers' alum sizing process,
by protecting the calcium carhonate particles with a
coating formed by adding a selected gellable hydrophilic
organic material to an aqueous suspension of the calcium
carbonate particles and thereafter causing the said
material to gel by means of a suitable gellant so as to form
aggregates of gelled hydrophllic material and calcium
carbonate particles. Under certain conditions aggregates
of a fibrous character may be formed. In such filliform
entities, a number of filler particles are associated with
one another and gelled in a linear form, so as to provide
the particles with a protective coating. The use of the
protected calcium carbonate ~iller is stated to give a
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1046815
slightly increased loading retention without reducing the
paper strength.
In German Offenlegungsschrift 2516097 it is
proposed to incorporate increased amounts of calcium
carbonate filler in paper without conse~uentially
reducing the strength of the paper by incorporating
into the paper pulp calciumcarbonate in the form of
a mixture of calcium carbonate with an aqueous latex
of a film~orming polymeric binder such as a styrene-
butadiene latex.
Since mineral fillers are considerably
cheaper than virgin cellulose fibre, it would be a
considerable commercial advantage if the filler content
of paper sheet could be ~ubstantially increased above
the maximum quantities presently possible whilst at the
same time maintaining the tensile strength and other
physlcal characteristics of the sheet.
Filler particles in solut~on or suspenslon
normally have an electrostatic charge. Generally the
filler particle will be negatively charged~ but in some
cases it may have a positive charge depending on the
hardness of the water, since an excess of positive ions
will be present if the water is hard.
SUMMARY OF ~HE INVENTION
We have now found in accordance with the present
invention that certain long chain relatively hlgh molecular
weight polymers have the capabillty of attracting thereto
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1046815
a plurality of filler particles so as to form a filler/
polymer conglomerate ln which the numerous filler particles
are retained in position by electrostatic attraction
between the filler particles and the polymer and by
polymer bridging effects, and that such conglomerates can
be used in the manufacture of paper sheet in order to
increase the filler content of the sheet without
sub~tantially affecting the physical strength character-
istics of the paper sheet, since the filler/polymer
conglomerates reduce the deleterious effect of the
filler on the hydrogen bonding of the fibres. We have also
found that such filler/polymer conglomerates are capable
of withstanding to a considerable degree the various
shear forces which are normally present in a conventional
papermaking system.
Thus in accordance with one ospect of
the invention, there is provided a method of manufacturing
paper sheet by means of a papermaking machine employing
an aqueous paper pulp containing a mineral filler,
characterized in that the mineral filler is incorporated
into the paper pulp in the form of a filler/polymer
conglomerate formed by contacting a particulate mineral
filler with a polymer having a zeta potential in the range
from -40 to +40 electron volts and a molecular weight of
at least 2 x 106.
In accordance with another-aspect of the invention,
there is provided as a novel composltion of matter a
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1~:)46815
filler/polymer conglomerate formed by contacting a
particulate mineral filler with a polymer having a
zeta potential in the range from -40 to ~40 electron
volts and a molecular weight of at least 2 x 106.
DETAILED DESCRIPTION OF THE INVENTION
The long chain relat~vely high molecular weight
polymers which are capable of forming such filler/polymer
conglomerates have a zeta potential ~ZP) in the range
from -40 to +40 electron volts (ev) and a molecular
weight of at least 2 x 106, preferably 2 x 106 to 20 x 106
and more preferably in the range from 4 x 106 to 12 x 106.
Advantageously the zeta potential is around zero or
slightly negative, i.e. in the range from ~5 to -20
ev~ and the molecular weight is in the range from about
5 to 10 x 106.
The zeta potential (or electrokinetic potential)
is defined as the electric potential across the diffuse
part of the double layer of ions surrounding a charged
particle in an ionic liquid, such as water. Thus
when for instance an electronegatively charged polymer
is dissolved in water, the polymer attracts a large
number of electropositive ions which form a thin
concentrated layer ad~acent thereto. Outside this thin
layer is a thicker more diffuse layer in which the
2g electropositively charged ions in the water are only
mildly attracted to the electrone~atively charged
polymer particle. It is the electric potential across
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1046815
thls diffuse layer which is termed the zeta potential.
Zeta potentlal can be measured using a 0.1% by
weight solution of the polymer in deionized water and an
electrophoresis device, for example a"Zeta-Meter" or
"Laser Zee Meter".
The polymers used in the present invention
may be positively or negatively charged depending
on the charge associated with the filler. Examples of
polymers which ha~e been found to give particularly
good results are high molecular weight polyacrylamides~
which may be homopolymers or copolymers of acrylamide.
The molecular weights of these polymers are conventionally
determined ~y intrinsic viscosity measurements in normal
(N) sodium chloride solutions.
The homopolymers of acrylamide, which are
normally essentially non-ionic,contain the repeating
unit:- R
--FCH2 -- 1--_
I
CONH2 n
wherein R is hydrogen (polyacrylamide) or methyl
~polymethacrylamide).
The copolymers of acrylamide may be anionic
in character, by the presence therein of a number of
anionic groups (Y) in place of some of the CONH2 groups,
or cationic in character, by the presence therein of a
number of cationic groups ~X~ in place of some of the
CONH2 groups. Thus the copolymers may contain the repeating
-7-
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.
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11~)46815
unit~:- R
CH2 - CH ~ ~CH
L CONH2J L Y~
or fC 2 IH l [CH2 - C
l CONH2~ m y
in which Y may represent, for example, a carboxylic
acid group (COOH) or an ammonium, alkali metal~ amine or
substituted amine salt of aid group, or an analogous
sulphonate salt; X may represent, for example, a
substituted amide group or a corre~ponding quaternary
ammonium salt cation thereof; and m and ~ may vary to
give a weight percent ratio between 100:0 and 50:50,
i.e. up to 50 mol % of anionic or cationic groups may be
present in the polymer. Alternatively the copolymers
may be non-ionic, if the copolymerizing monomer is a non-
ionic vinyl monomer such as, for example, acrylonltrile
or ethyl acrylate. Such copolymers of acrylamide may
have molecular weights in the range from 2 to 20 x 106.
The size of the filler/polymer conglomerate
will depend on the particular polymer used, but can be
varied by ad~usting the weight ratio of polymer to filler.
For example the conglomerate may contain from 0.01 to 0.5
by weight of dry polymer, based on dry weight of filler.
Preferably the conglomerate has an average diameter in
the range from 50 to 100 microns. Advantageously the
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10468~5
conglomerates are of a size such that upon being
sub~ected to shear forces, such as experienced on a
papermaking machine, at least the major proportion thereof
will assume a filliform shape which enhances the
hydrogen bonding of the cellulose fibres and the
filler retention without detracting from the appearance
of the paper sheet.
The mineral filler used in the production of the
filler/polymer conglomerate may be, for example, calcium
carbonate, which may be used in any of its com~ercially
available forms such as, for example, natural chalk
whiting. Alternatively, the filler may be, for example,
china clay, talc or titanium dioxide. If desired a
mixture of different fiLlers may be used.
The filler/polymer conglomerates of the invention
can be prepared by adding the polymer, preferably in the
form of a solution in water, to an aqueous suspension of
the filler containing, for example, rom 20 to 35% by
weight of filler and, if desired, applying a low
shearing force to the resulting mixture, for example
by passing the m~xture through a static mixer, in order
to reduce any variation in the particle size of the
conglomerates. The production of the conglomerates
can be carried out batchwise or contlnuously, and the
size of the conglomerate particles can be ad~usted by
varying the rate of ~ddition of the polymer. The conglomer-
ates produced in this manner can then be used in an otherwise
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conventional papermaking s~stem in place of the normal
filler particles. Thus they can be incorporated in the
furnish before the lateer is applied to the wet end of
the papermaking machine in a known manner. If requlred,
the conglomerates can be passed through one or more
additional shearing devices, for example stock cleaners,
mechanical screens or fan pumps, in w Sch they can be
sub~ected to an ad~ustable shear force~ prior to being
fed into the papermaking system.
Advantageously the conglomerates are prepared
by continuous addition of an aqueous solution of the
high molecular weight polymer, for example a high
molecular we~ght substantially non-ionic polyacrylamide
solution, to a flowing aqueous suspension of mineral
flller, for example calcium carbonate, and then passing
the resulting aqueous suspension of filler-polymer
conglomerates through a static mixer, from which the
resulting low sheared co~glomerate suspension can be fed
tinto a flowing aqueous paper pulp which is being fed
to the wet end of a papermaking machine. When preparing
and using the conglomerates in the foregoing continuous
manner, it is advantageous to feed the conglomerate
suspension into the papermaking system through a feed
pipe at least part of which is transparent so that the
particle size and structure of the conglomerates can be
observed and if necessary ad~usted.
If desired, conventional wet-strength or dry-
strength resins or a starch (which may be an oxidised
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`` ~046815
starch) can be present during the formation of the
filler/polymer conglomerates, s~nce it has been found
that the presence of such resins or starch helps to
improve still further the mechanical stability which the
conglomerates normally possess to a considerable degree
as previously mentioned. Examples of such resins are
polyamide-epichlorohydrin or polyam~de/polyamine
epichlorohydrin wet strength resins and melamine
formaldehyde dry-strength resins. The latter may be
sulphited so as to be alkaline and anionic in charge. These
resins, or starch, may be added either to the polymer
or to the aqueous filler suspension prior to the contacting
of the filler and the polymér. Wet and dry strength resins
are normally commercially available in the form of
aqueous solutions and nu~ be added in an amount of,
for example, from 0.02 to 0.8 weight % of aqueous solution,
based on the weight of polymer.
The papermaking process of the invention can `
be carried out using a conventional furnish formed
partly from hardwood and p~rtly~from ~oftwooà and
if de~ired cincorporating an internal sizing agent, for
example an aqueous ketene dimer emulsion such as the
commercially available product "Aquapel" marketed in the
United Kingdom by Hercules Powder Company Limited.
The filler~polymer conglomerates produced in
accordance with the invention cna be employed in an
alkaline papermaking system, i.e. a system in which the
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`' ~0468~5
paper stock is maintained at an alkaline pH value;
alternatively thè filler/polymer conglomerates may be
used in an acid papermaking system, i.e. one having paper
stock at an acid pH value, either with an inert filler
such as china clay or surprisingly even with a filler
which is normally reactive in an acid system, such as
ca~cium carbonate which is relatively cheap and readily
available, since conglomerates formed with calcium
carbonate in accordance with the invention have surprisingly
been found to exhibit substantial resistance tos~tid attack.
It has been found that by using filler/polymer
conglomerates in accordance with the invention, it is
possible to increase the filler content ~in the finished
paper sheet by a value in~the range from 25 to 60%
increase compared with paper formed with normal filler
and yet msintain the strength and other physical properties
desired in the finished paper sheet. Thus as a result
of the invention it is possible to replace relatively
expensive virgin cel~ulose fibre by relatively cheap
filler.
The following non-limitative Examples illustrate
how the invention may be carried into effect.
EXAMPLE 1
This Example illustrates the use of the invention
in an alkaline papermaking system with whiting as filler.
A paper pulp furnish was made up in a conventional
msnner from fully bleached chemical pulps snd recycled
1046815
broke (made from a similar furnish), so that the furnish
comprised 34 weight % of hardwood, 36 weight X of softwood
and 3~ of the recycled broke. An alkaline internal
sizing agent, namely the commercially available product
"Fibran" marketed in the United Kingdom by Laing-National,
was incorporated in the furnish, which then had a pH of 7.2.
A commercially available homopolymer of acrylamide
(having a zeta potential of -14 ev (measured with a 0.1~
by weight solution in distilled water on a Laser Zee Meter),
a molecular weight of about 8 x 10 and a viscosity
equal to 92 c.p. units at 15C. measured with a 0.5~
by weiqht solution on a RVT Brookfield Viscometer at
50 r.p.m.) was dissolved in city water (having a
total hardness of appro~imately 300 ppm.) to give a 0.5~
w/w solids pGlyacrylamide solution. The viscous solution
produced in this manner was pumped at a flow rate of
about 180 litres per hour through a positive displacement
pump into a feed line through which was passing a
25% w/w aqueous slurry of natural chalk whiting (calcium
carbonate) filler (sold in the United Kingdom as
S N owcAL ('rr~d e m ~I l` ~)
~4~c61 8.SW by The Cement Marketing Company Limited)
at a flow rate of 30 litres per minute, so as to give
a percentage addition of polymer solution to wet filler
flow of about 10~. The polyacrylamide solution was fed
into the filler feed line immediately after the dilution
water additlon point and ~ust before a static mixer. The
dilution water was fed int~ the filler feed line at a
. . .
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"- ~0468~s
rate such as to give a dilution factor of about 3 to l.
The effluent from the static mixer which
comprised chalk whiting/polyacrylamide conglomerates
suspended in water, the conglomerates having an average
diameter in the range of 50 to lOO microns, was fed
through a transparent plastics pipe into the thinstock
flow in the approach flow shortly before the flowbox. A
solution in water of a polyamine retention aid, namely
the com~ercially available product "NATRON (Trademark) 88"
(sold in the United Kingdom by Lain-National) was added
immediately the flowbox to retain fines and to~maximise
size retention.
Cream wove paper was then produced on a
papermaking machine using a slightly alkaline system
having a zeta potential of about zero. Paper was produced
at 400Kg. per hour at the reel end at a reel end
speed of 242 metres per minute.
The following Table indicates the physical
results obtained with the paper produced in accordance -
with the invention as described in the foregoing Example
compared with the results obtained with paper produced
in an identical manner save that untreated calcium
carbonate filler was used in the conventional manner
instead of the filler/polymer conglomerates.
_14-
Basis % total Basis Burst Breaking
weight` ash weight strength length
(sheet) (fibre) based on metres on
~sm gsm 100 g. fibre sheet
Conglomerate 80 29 56.8 396 6210
CaCO3 filler 75 18 61.5 390 6170
~ It can be seen from the foregoing results that
by employing the present invention the fil8~r content
of the paper sheet was substantially increased without any
deterioration in the sheet strength.
EXAMPLE 2
This Example illustrates the use of the
invention in an alkaline papermaking system with china
clay as filler.
Teleprinter paper was protuced in a manner
similar to that described in Example 1 except that LEE NOOR
(Trademark) grade B lump china clàj (English Clays Lovering Pochin
~ Co. Limited) was used in place of the natural chalk
whitinggfiller.
The following Table illustrates the physical
results obtained compared with the results obtained using
untreated china clay in the conventional manner.
Basis X total Basis Burst Breaking
weight ash weight stsength length
(sheet) (fibre) based on metres on
~sm gsm 100g.;flb~heet
fibre
Conglomerate 73.0 20 58.4 275 6520
China clay 70.5 14 60.7 231 5500
It can be seen from the foregoing results that
by use of the invention, the filler content was substantially
-15-
1046815
increased without any deterioration in the physical
strength properties of the sheet.
EXAMPLE 3
This Example illustrates the use of the
invention in an acid papermaking system with ~hiting as
filler and a wet strength resin present during formation
of the filler/polymer conglomerates.
A paper pulp furnish was made up in a
conventional manner from fully bleached chemical pulps
and recycled broke (made from a similar furnish), so
that the furnish comprised 45 weight % of hardwood,
40 weight % of softwood and 15% of the recycled broke.
A rosin/alum sizing aget was incorporated in the furnish,
which then had a pH of about 6.3. 7
A commercially available non-ionic ho~opolymer
of acrylamide (having a molecular weight of about 5 x 106
and a viscosity equal to 82 c.p. units at 15C. measured
with a 0.5 % by weight solution on a RVT Brookfield
Vi~cometer at 50 r.p.m.) together with 0.05% by~weight~
based on the welght of polyacrylamide, of a commercially
available aqueous solution of a polyamide-epichlorohydrin
wet-strength resin (sold in the United Kingdom as KYMENE (Trademark)
557 ~y Hercules Pow~ër Company Limited) were dissolved
in city water to give a 0.3% wlw solids polyacrylamide
sollution having a zeta potential of -2ev. The viscous
solution produced in this manner was pumped at a flow
rate of about 80 litres per~hour through a positive
104681~
displacement pump into a feed line through which was passing
z 35% w/w aqueous slurry of natural chalk whiting (calcium
carbonate) filler (sold in the United Kingdom as Snowcal
4ML by The Cement Narketing Company Limited) at a flow
rate of 900 litres per hour, so as to give a percentage
addition of polymer solution to wet filler flow of about
8.8Z. The polyacrylamide solution was fed into the filler
feed line and the resultant mixture fed through a static
mixer to ensure thorough blending.
The effluent from the static mixer which
comprised chalk whiting/acrylamide conglomerates suspended
in water, the conglomerates having an average diameter
in the range of 60 to 65 microns, was fed through a
transparent plastics pipe into the second stage cleaners
for the furnish. A solution in water of a polyacrylamide
retention aid, namely the commercially available
product PERCOL (Trademark) (sold in the United Kingdom by Allied
Colloids) was added i~mediately before the flowbox to
retain fines and to maximise size retention.
High quality board was then produced on a
papermaking machine using a slightly acid system
having a zeta potential of approximately zero. Paper was
produced at 1850 Kg. per hour at the reel jend at a reel
end speed of 95 metres per minute.
The following Table indicates th~ physical
results obtained with the board produced in accordance
with the invention as described in the foregoing Example
-17-
10~;8i5
compared with the results obtained with board produced in
an identical manner save that untreated calcium carbonate
filler was used in the conventional manner-instead of
the filler/polymer conglomerates.
Basis % total Basis Burst Breaking
weight ash weight strength length
(sheet) (fibre) based on metres on
gsm _ gsm lOOg. sheet
fibre
Conglomerate 146 18.7 118 284 6525
CaC03 filler 150 13.7 136.5 260 6480
It can be seen from the foregoing results that
by employing the present invention, the filler content
of the paper sheet was substantially increased without
any deterioration in the sheet strength. Thus the
percentage increase on ash content was 36Z, whilst the
percentage increases on burst strength and breaking
length (i.e. tensile strength) were 9.2% and 0.6%
respectively.
It should also be noted that in this process,
no problems were caused by the use of whiting as filler
in an acid system as normally occur with whiting in
its conventional form.
EXAMPLE 4
This Example ~llustrates the use of the
invention in an acid papermaking system with china clay
as filler and a wet strength resin present during
formation of the filler/polymer conglomerates.
A paper pulp furnish was made up in a
convention manner from fully bleached chemical pulps
-18-
and recycled broke (made from a similar furnish),
so that the furnish comprised 55 weight % of hardwood,
35 weight % of softwood and 10 % of the recycled broke.
Sufficlent rosin/alum sizing agent was incorporated
in the furnish to give a pH value of 5.5.
A commercially available homopolymer of
acrylamide (having a molecular weight of about 5 x 106
and a vis60s~ty equal to 82 c.p. units at 15C. measured
with a 0.5 % by weight solution on a RVT Brookfield
Viscometer at 50 r.p.m.) together with 0.05% by weight,
based on the weight of polyacrylamide, of a commercially
available aqueous solution of a polyamide-epichlorohydrin
wet-strength resln (sold in the United Kingdom as Kymene
557 by Hercules Powder Company L~ited) were added to city
water to give a 0.3% w/w solids polyacrylamide solution
hsiing a zeta potential of +luv. The viscous solution
produced in this manner was pumped at a flow rate
of about 220 litres per hour through a positive -
displacement pump into a feed line through which was
passing a 25X w/w aqueous slurry of filler grade china
clay at a flow rate of 2450 litres per hour, so as to
give a percentage addition of polymer solution to wet filler
flow of about 9.0%. The polyacrylamide solution was
fed into the filler feed line and the resultant mixture
fed through a static mixer to ensure thorough blending.
The effluent from the sta~ic mixer which
comprised china clay/polyacrylamide conglomerates suspended
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~46815
in water, the conglomerates having an average diameter
in the range of 50 to 55 microns, was fed through
a transparent plastics pipe into the papermaking system
at a point before the mechanical screens for the furnish.
A solutiQn in water of a polaymide retention aid,
namely the commercially available product RETAMINOL (Trademark)
C ~sold in the United Kingdom by Bayer) was added
immediately before the flowbox to retain fines and to maxi-
mise size retention.
Woodfree continuous stationery w~s then
produced on a papermaking machine using an acid system
having a slightly positive zeta potential. Paper was
produced at 4200 Kg. perhour at the reel end at a reel
end speed of 600 metres per minute.
The following Table indicates the physical
results obtained with the paper produced in accordance
with the invention as described in the foregoing Example
compared with the results obtained with paper produced in
an identical manner save that untreated china clay f$11er
was used in the conventional manner instead of the filler/
polymer conglomerates.
Basis % t`otal Basis Burst Breaking
weight ash weight strength length
(sheet) (fibre) based on metres on
~sm ~sm 100g. fibresheet.
Conglomerate 53.1 14 45.66 199 4850
China Clay 52.0 9 47.3 197 4450
filler
It can be seen from the foregoing results that
by employing the present invention, the filler content
-20-
10468~S
of the paper sheet was substantially increased without
any deterioration in the sheet strength. Thus the
percentage increase in ash content was 55.5Z, whilst the
percentage increases in burst strength and breaking
length (or tensile strength) were 1.0% and 8.9Z respecti~ely.
EXANPLE 5
This Example illustrates the use~of the
invention in an acid paper~aking system with china clay
as filler.
A paper pulp furnish was made up in a
conventional manner from f~lly bleached chemical
pulps and recycled broke (made from a similar furnish),
so that the furnish comprised 55 weight % of hardwood,
35 weight % of softwood and 10% of the recycled broke.
Sufficient rosin/alum sizing agent was incorporated in the
furnish to gi~eea pH value of 5.5.
A commercially available homopolymer of
acrylamide (having a molecular weight of about 5 x 106
and a viscosity equal to 82 c.p. units at 15C. measured
with a 0.5 % by weight solution on a RVT Brookfield -
Viscometer at 50 r.p.m.) was dissolved in city water
to give a 0.3% w/w solids polyacrylamide solution having
a zeta potential of ~lev. The viscous solution produced
in this manner was pumped at a~flow rate of about 220 litres
per hour through a positive displacement pump into a feed
line through which was passing a 25% w/w aqueous slurry
of filler grade china clay at a flow rate of 2450 litres
-21-
--` 10468~5
per hoor, so as to give a percentage addition of polymer
solution to wet filler flow of about 9Ø The polyacrylamide
solution was fed into the filler feed line and the
resultant mixture fed through a static mixer to ensure
thorough blending.
The effluent from the static mixer which
comprised china clay/polyacrylamide conglomerates -
suspended in water, the conglomerates having an average
diameter inthe range of 25 to 35 microns, was fed
through a transparent plastics pipe into the papermaking
system at a point before the mechanical screens for the
furnish. A solution in water of a retention aid, the
commercially available product Retaminol C (sold
in the United Kingdom by Bayer) was added immediately
~before the flowbox to retain fines and to maximise size
retention.
Woodfree continuous stationery was then produced
on a papermaklng machine using an acld sy~tem havlng a
sllghtly posltlve zeta potentlal. Paper was produced
at 4200 Kg. per~hour at the reel end at a reel end speed
of 600 metres per minute.
The followlng Table lndicates the physical
results obtained with the paper produced in accordance
with the invention as described in the foregoing Example
compared with the results obta$ned with paper produced in
an identical manner save that untreated china clay filler
was used in the conventional manner instead of the filler/
-22-
~046B15
polymer conglomerates.
Basis Z total Basis Burst Breaking
weight ash weight strength length
(sheetj (fibre) based on metres on
~sm gsm lOOg. fibre sheet
Conglomerate 52.5 12 46.2 197 4500
China Clay 52.0 9 47.3 197 4450
filler
It can be seen from the foregoing results that
by employing the present invention, the filler content
of the paper sheet was substantially increased without
any deterioration.in the sheet strength. Thus the
percentage increase on ash content was 33.3Z, whilst
the percentage increases on burst strength and breaking
length were about 1% and 5Z respectively.
EXANPLE 6
This Example illustrates the use of the
invention in an acid papermaking system with china -
clay as filler and a dry strength resin present during
formation of the filler/polymer conglomerates.
A paper pulp furnish was made up in a
conventional manner from fully bleached chemical pulps
and recycled broke (made from a similar furnish), so
that the furnish comprised 10 weight Z of hardwood,
80 weight % of softwood and 10% of the recycled broke.
A fortified rosin/alum sizing agent was incorporated in the
furnish so as to give a pH of about 5.8.
A commercially available homopolymer of
acrylamide (having a molecular weight of about 5 x 106
and a viscosity equal to 82 c.p. units at 15C. measured
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` ~0468~
with a 0.5Z by weight solution on a RVT Brookfield
Viscometer at 50 r.p.m.) together with 0.5% by weight, based
on the weight of polyacrylamide, of a commercially available
aqueous solution of a sulphited melamine formaldehyde
dry-strength resin (sold in the United Kingdom by British
Industrial Plastics Limited) were added to city water
to give a 0.4~ w/w solids polyacrylamide solution having
a zeta potential of -20ev. The viscous solution produced
in this manner was pumped at a flow rate of about
186 litres per hour through a positive displscement
pump lnto a feed line through wh~ch~w~svp~ing a~20X
w/w aqueous slurry of china clay at a flow rate of 1550
litres per hour, so as to give a percentage addition
of polymer solution to wet filler flow of about 20%.
The polyacrylamide solution was fed into the filler feed
line and the resultant mixture fed through a static mixer
to ensure thorough blending.
The effluent from the static mixer which comprised
~china clay/polyacrylamide conglomerates suspended in water,
the conglomerates having an average diameter in the range
of 85 to 95 microns, was fed through a transparent
plastics pipe into the flowbox manifold of a paper~aking
machine. No retention aid was added to the furnish.
Paper of sugar bag liner grade was then produced
on the papermaking machine using àn acid system having a
slightly positive :~eta potenti~l. Paper was produced
at 2000 Kg. per hour at the reel end at 8 reel end speed
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~(~4681~;
of 100 metres per minutes.
The following Table indicates the physical
results obtained with the paper produced in accordance
with the invention as described in the foregoing Example
compared with the results obtained with paper produced in
an identical manner save that untreated china clay
filler was used in the conventional manner instead of
the filler/poly~er conglomerates.
Basis % total Basis Burst Breaking
weightash weight strength length~
~sheet) (fibre) based on metres on
~sm ~sm lOOg. fibre sheet
Conglomerate 67.2 12.3 59.1 440 7820
China clay 64.68.7 59.0 424 6330 -
filler
It can be seen from the foregoing results
that by employing the present invention, the filler
content of the paper sheet was substantially increased
without any deterioration in the sheet strength. Thus the
percentage increase in ash content was 34.5%, whilst
the percentage increases in burst strength and breaking
length (or tensile strength) were 3.7% and 23.5%
respectively.
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